The present invention relates to an apparatus for preventing the formation of alkane hydrates in subsea oil and gas production equipment. More particularly, the invention relates to such an apparatus which comprises one or more heating cables to maintain the produced well fluid in the production equipment above a predetermined temperature below which alkane hydrates will form.
Subsea oil and gas wells which are located at depths greater that 5,000 feet or at extreme latitudes are exposed to water which is typically just a few degrees above freezing. Although the well fluid is relatively hot as it flows through the subsea production equipment, the surrounding water will cool the fluid rapidly when the flow is interrupted for any length of time, such as by a temporary well shut down. If the well fluid is allowed to cool to below the hydrate formation temperature of the fluid, which averages about 70xc2x0 F. for typical hydrocarbons, alkane hydrates may form in the fluid which may block the flow paths through the production equipment.
In the prior art, thermal insulation materials have been used on the subsea equipment to retard the cooling of the well fluid until flow can be restored or a hydrate inhibitor can be injected into the fluid. However, several inches of insulation are usually required to provide the necessary thermal barrier, and this affects the design and manufacture of the subsea equipment and adds significantly to the cost of the equipment. In addition, the hydrate inhibitor and the equipment required to inject it into the fluid are relatively expensive.
The present invention addresses these and other disadvantages in the prior art by providing a heating device for preventing the formation of alkane hydrates in a subsea oil and gas production equipment component having at least one flow path through which a well fluid is permitted to flow. The heating device comprises at least one heating cable which is positioned in heat exchange relation with respect to the flow path, a source of electrical power connected to the heating cable and an insulation layer disposed over the heating cable and the component. When the temperature of the well fluid in the component drops to a point below its flow temperature, the heating cable will generate heat and this heat will be transferred to the well fluid to maintain the temperature of the well fluid above its hydrate formation temperature. The insulation layer helps to direct the heat from the heating cable into the component and also serves to seal and protect the heating cable from the ambient water. The heating cable is preferably self-regulating, that is, it increases its heat output as the temperature of the heating cable drops and decreases its heat output as the temperature rises. Alternatively, the heating device could also comprise a thermostat to energize the heating cable when the temperature of the well fluid drops below a first predetermined temperature and deactivate the heating cable when the temperature rises above a second predetermined temperature. Thus, the heating device effectively maintains the temperature of the well fluid above its hydrate formation temperature without the need for bulky insulation or costly hydration inhibitors.
These and other objects and advantages of the present invention will be made more apparent from the following detailed description, with reference to the accompanying drawings. In the drawings, the same reference numbers are used to denote similar components in the various embodiments.